Degenerative joint disease or osteoarthritis (OA) is one of the most common disabling diseases affecting middle-aged and older people. It is characterized by the breakdown of an unstable matrix network in cartilage. To better understand the pathogenic process of OA, it is necessary to examine how the matrix structure is stabilized in mature cartilage, and what causes destabilization of such a structure. The long term career goal of the candidate is to analyze the molecular mechanisms of stabilizing matrix networks in mature cartilage. The immediate research plan is to determine the role of cartilage matrix protein (CMP), a mature cartilage specific protein that interacts with both collagenous and non-collagenous matrix components to form a filamentous network, in the stabilizing process. As a newly independent investigator, the candidate is applying for an RCA to protect his research time at 95 percent level and to continue his productive record. This proposal for the next five years of research is based on candidate's recently funded FIRST Award from NIH and the Arthritis Investigator Award from Arthritis Foundation. It contains four specific aims: 1) To characterize the interaction sites between CMP and matrix network. The location and properties of the adhesion sites will be determined by examining the interaction of a series of recombinant CMPs with matrix networks in a primary chondrocyte culture. 2) To analyze the nature of the covalent crosslinking of CMP in cartilage matrix. A monoclonal antibody will be used to determine whether CMP is a substrate for tissue transglutaminase. 3) To determine whether the disruption of interaction and crosslinking of CMP will result in a misassembled or unstable matrix network that is subject to degeneration. The dominant negative CMP constructs will be expressed in cartilage by retroviral infection. The effects will be examined by immunohistochemical analysis. 4) To examine whether abnormal CMP gene expression in human OA articular cartilage leads to a defective matrix structure. In situ hybridization and electron microscopy will be used to analyze abnormal synthesis and assembly of CMP in OA cartilage. These data will contribute not only to our basic understanding of cartilage matrix assembly, but also to the development of methods for prevention and treatment of cartilage degeneration.